1. Field of the Invention
The present invention relates to an automation system and, more particularly, to a method of operating an automation system comprising an automation device connected for communication with a central unit.
2. Description of the Related Art
In an automation system, the automation units connected for communication and the central unit, or each central unit provided for their control, are intended for an automation solution and accordingly control and/or to monitor a respective technical process to be automated. As well as the communication users encompassed by the automation system, a significant component is the network provided to connect them for communication. To link it to this network, each communication user has a bus connection. In an automation system with an underlying network, e.g. Ethernet, Institute of Electrical and Electronic Engineers (IEEE) Standard 802.3, Wireless Local Access Network (WLAN) IEEE Standard 802.11 or CAN, in which the communication is handled, for example, by a communications protocol such as PROFINET, each device has a bus connection for connection to the network and a projected position of the respective device in a hierarchy of the automation system determines individual devices as masters (IO controller) and other devices as slaves (IO device). In an automation system, the central unit occupies a particular hierarchical position so that at least the central unit functions in the network as a master or IO controller. Examples of slaves, on the other hand, are periphery modules, sensors and actors with bus capabilities etc. which occupy a subordinate position in the hierarchy of the automation system compared to the central unit. Data is exchanged between IO controller and IO devices by means of cyclic real-time communication. For such real-time communication the continuous time is broken down into consecutive cyclic time segments of the same duration, meaning that the natural continuous time is thus discretized. These time segments are referred to below as send clocks. Communication users, i.e., IO controller and IO devices, which exchange data with each other with this type of cyclic real-time communication, previously had to be operated with the same send clock. This previously made it necessary for the central unit or each central unit, i.e., the IO controller or each IO controller, always to be operated with a send clock which is supported by all other automation devices (IO devices) encompassed by the automation system. Generally, the result of this is that, in system configurations in which devices support different send clocks, those system users that support faster/higher send clocks are not able to be operated with these faster/higher send clocks if users exist that do not support this send clock. Usually, newly developed IO controllers support more send clocks than the IO devices already included in an automation solution/an automation system, especially faster or higher send clocks. If a system operator wants to exploit the higher performance or the new IO controllers, until now an update, i.e. a firmware update, for example, has had to be performed on various IO devices or the IO devices themselves are to be replaced by newer IO devices with correspondingly improved communication capabilities.
European Patent EP 1527578 B1 and European Publication EP 2133763 A1 both disclose methods for communication between an IO controller and IO devices for the special case of integer ratios of the send clock of each of the IO devices and the send clock of the IO controller.
In large automation systems, especially with many different devices, the integer ratios named above are often difficult or even impossible to fulfill and the system has to be run very often in a non-optimum range and/or has to be slowed down drastically to properly work.